Add theming and a Windows 3.11 inspired theme.

Marechai.App/Services/ColorThemeService.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Windows.Storage;
+using Microsoft.UI.Xaml;
+using Uno.Extensions.Toolkit;
+
+namespace Marechai.App.Services;
+
+public interface IColorThemeService
+{
+    string                CurrentColorTheme    { get; }
+    IReadOnlyList<string> AvailableColorThemes { get; }
+    void                  ApplyColorTheme(string        themeName);
+    void                  SetThemeService(IThemeService themeService);
+    void                  ReapplyCurrentTheme();
+}
+
+public class ColorThemeService : IColorThemeService
+{
+    private const string        COLOR_THEME_KEY = "ColorTheme";
+    private const string        DEFAULT_THEME   = "Default";
+    private       IThemeService _themeService;
+
+    public ColorThemeService()
+    {
+        LoadSavedTheme();
+    }
+
+    public string CurrentColorTheme { get; private set; } = DEFAULT_THEME;
+
+    public IReadOnlyList<string> AvailableColorThemes => new List<string>
+    {
+        DEFAULT_THEME,
+        "Windows311"
+    };
+
+    public void SetThemeService(IThemeService themeService)
+    {
+        _themeService = themeService;
+
+        // Reapply the current theme now that we have the theme service
+        if(CurrentColorTheme != DEFAULT_THEME) ReapplyCurrentTheme();
+    }
+
+    public void ReapplyCurrentTheme()
+    {
+        // Force refresh of the current theme
+        ApplyColorTheme(CurrentColorTheme);
+    }
+
+    public void ApplyColorTheme(string themeName)
+    {
+        if(!AvailableColorThemes.Contains(themeName)) return;
+
+        CurrentColorTheme = themeName;
+
+        // Save preference
+        try
+        {
+            ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings;
+            localSettings.Values[COLOR_THEME_KEY] = themeName;
+        }
+        catch
+        {
+            // Silently fail
+        }
+
+        // Apply the theme by rebuilding merged dictionaries
+        Application app = Application.Current;
+
+        if(app?.Resources == null) return;
+
+        // Store the existing merged dictionaries (except color overrides)
+        var existingDictionaries = app.Resources.MergedDictionaries
+                                      .Where(d => d.Source?.OriginalString?.Contains("ColorPaletteOverride") != true)
+                                      .ToList();
+
+        // Clear all merged dictionaries
+        app.Resources.MergedDictionaries.Clear();
+
+        // Re-add the existing dictionaries
+        foreach(ResourceDictionary dict in existingDictionaries) app.Resources.MergedDictionaries.Add(dict);
+
+        // Add the new color theme if not default
+        if(themeName != DEFAULT_THEME)
+        {
+            var newDictionary = new ResourceDictionary
+            {
+                Source = new Uri("ms-appx:///Styles/ColorPaletteOverride.xaml")
+            };
+
+            app.Resources.MergedDictionaries.Add(newDictionary);
+        }
+
+        // Force UI refresh by toggling the theme temporarily
+        ForceThemeRefresh();
+    }
+
+    private void LoadSavedTheme()
+    {
+        try
+        {
+            ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings;
+
+            if(localSettings.Values.ContainsKey(COLOR_THEME_KEY))
+            {
+                var savedTheme = localSettings.Values[COLOR_THEME_KEY] as string;
+
+                if(!string.IsNullOrEmpty(savedTheme) && AvailableColorThemes.Contains(savedTheme))
+                {
+                    CurrentColorTheme = savedTheme;
+                    ApplyColorTheme(CurrentColorTheme);
+                }
+            }
+        }
+        catch
+        {
+            // If loading fails, use default theme
+        }
+    }
+
+    private async void ForceThemeRefresh()
+    {
+        if(_themeService == null) return;
+
+        try
+        {
+            // Get current theme
+            AppTheme currentTheme = _themeService.Theme;
+
+            // Toggle to opposite theme briefly
+            AppTheme tempTheme = currentTheme == AppTheme.Light ? AppTheme.Dark : AppTheme.Light;
+            await _themeService.SetThemeAsync(tempTheme);
+
+            // Small delay to ensure the change is applied
+            await Task.Delay(50);
+
+            // Switch back to original theme
+            await _themeService.SetThemeAsync(currentTheme);
+        }
+        catch
+        {
+            // Silently fail
+        }
+    }
+}